Optical displays, such as liquid crystal displays (LCDs), are becoming increasingly commonplace, finding use for example in mobile telephones, portable computer devices ranging from hand held personal digital assistants (PDAs) to laptop computers, portable digital music players, LCD desktop computer monitors, and LCD televisions. In addition to becoming more prevalent, LCDs are becoming thinner as the manufacturers of electronic devices incorporating LCDs strive for smaller package sizes.
Many LCDs use a backlight for illuminating the LCD's display area. The backlight can include a solid lightguide in the form of a slab or wedge. The solid lightguide is often made of an optically transparent polymeric material produced by, for example, injection molding. Many solid lightguides also include a reflector that is used to more efficiently utilize light that may exit the bottom surface of the solid lightguide. The backlight can instead include a hollow cavity lightguide which has reflective surfaces surrounding the interior of a hollow cavity. The output surface of the hollow cavity lightguide is often a partially transmissive surface.
In many applications, the backlight includes one or more light sources that optically couple light into the lightguide from one or more edges of the lightguide. The optically coupled light typically travels through a solid lightguide by total internal reflection (TIR) from the top and bottom surfaces. The optically coupled light travels through the hollow cavity lightguide by reflection from reflective surfaces. Eventually, the light encounters some feature that causes a portion of the light to exit the lightguide through an output surface. The feature can be an extraction surface that re-directs light through the output surface, or the output surface can be a partial reflector that allows a portion of the light to leak from the lightguide with each reflection.
Backlight reflectors used in both solid and hollow cavity lightguides need to have a high reflectivity for efficient transport of light. An efficient reflector is a multilayer interference reflector available from 3M Company under the trade designation Vikuiti ESR™ (Enhanced Specular Reflective) film. High reflectivity is achieved using a suspended ESR film that has a low index material (typically an air gap) adjacent to each surface of the film. There is a need for a method to secure highly reflective interference reflector films to surfaces, while maintaining the air gap adjacent to each side of the film.